Paper 1- Physical Chemistry

Question 1

What is an exothermic reaction?

Answer 1

A reaction that gives out energy to the surroundings resulting in a rise in temperature of the surroundings

-EXothermic- EXIT- gives out

Question 2

What is an endothermic reaction?

Answer 2

A reaction that takes in energy from surroundings resulting in a decrease in temperature of the surroundings

-ENdothermic-enter-take in

Question 3

What is enthalpy change?

Answer 3

overall change in energy in a reaction

Question 4

Does enthalpy change have a positive or negative value when the reaction is exothermic

Answer 4

• negative

- as the reaction is giving out energy

Question 5

Does enthalpy change have a positive or negative value when the reaction is endothermic

Answer 5

• positive

- as reaction takes in energy

Question 6

What is the rate of a reaction?

Answer 6

how fast the reactants are changed into products

Question 7

Give an example of a slow reaction?

Answer 7

rusting of iron

Question 8

Give an example of a moderate reaction?

Answer 8

metal magnesium reacting with an acid

Question 9

Give an example of 2 fast reaction?

Answer 9

burning and explosions

Question 10

How do you find speed of a reaction?

Answer 10

By recording the amount of product formed or amount of product used up over time

Question 11

What does a steeper line on the graph show in terms of rate of reaction

Answer 11

fast reaction

Question 12

What does the rate of a reaction depend on?

Answer 12

• collision frequency of reacting particles (the more collisions, the faster reaction)
• energy transferred during a collision (particles have to collide with enough energy for the collision to be successful

Question 13

What is activation energy?

Answer 13

the minimum amount of energy that particles need to react

Question 14

Why do particles need activation energy?

Answer 14

-to break the bonds in the reactants and start the reaction

Question 15

What four factors does the rate of reaction depend on?

Answer 15

• temperature
• concentration
• surface area
• catalyst

Question 16

How does increasing the temperature increase the rate of reaction?

Answer 16

• when temperature is increased particles move faster so will have more collisions
• higher temp also increases energy of collisions, as particles are moving faster
• meaning at higher temps there will be successful collisions
• so increasing the temp increases rate of reaction

Question 17

Explain why increasing concentration increases the rate of reaction

Answer 17

-if a solution is more concentrated it means there are more particles of reactant in same volume making collisions more likely so ROR increases

Question 18

Explain why increasing pressure increases the rate of reaction

Answer 18

-increasing pressure in a gas means particles are more crowded so frequency of collisions between particles will increase

Question 19

Explain why increasing surface area increases the rate of reaction

Answer 19

• breaking a solid into smaller pieces will increase its surface area to vol ratio
• meaning particles around it will have more area to work on
• meaning rate of reaction is faster for solids with a large surface area to vol ratio

Question 20

What is a catalyst?

Answer 20

a substance which increases the rate of reaction without being chemically used up or changed in a reaction,

-usually finds an alternate pathway

Question 21

How do catalysts work?

Answer 21

• lower the activation energy by providing an alternative pathway that has a lower activitaion energy
• as a result more particles have the minimum amount of energy needed for reaction to occur when particles collide

Question 22

How can you show the effect of a catalyst

Answer 22

Reaction profiles

Question 23

Name the equation used to measure the speed of a reaction

Answer 23

amount of reactant used or amount of product formed / time

Question 24

Name the three rates of reaction experiments

Answer 24

• precipitation
• change in mass
• volume of gas given off

Question 25

Describe what occurs in the precipitation experiment?

Answer 25

• two see through solutions produce precipitate
• mix the two reactant solutions in conical flask
• put conical flask over paper with a cross on it
• measure how long it takes for cross to disappear
• the faster the cross disappears the faster the reaction

Question 26

Describe what occurs in the change in mass experiment?

Answer 26

• as gas is released, mass decreases
• you know reaction has finished when the reading on the mass balance stops
• quicker the reading on the balance drops, the faster the reaction

Question 27

Describe what occurs in the volume of gas given off experiment?

Answer 27

• use gas syringe to measure volume of gas given off
• you know reaction has finished when reading on balance stops changing
• the more gas given off in a set time interval, the faster the reaction

Question 28

Describe the method used to measure how surface area effects rate?

Answer 28

• set appartus up with marble chips and dilute HCL in a conical flask with a bung. Have a tube coming out of the bung to a gas syringe
• measure vol of gas produced using gas syringe
• take readings at regular intervals
• repeat experiment

Question 29

Why does finer particles of a solid lead to a higher rate of reaction

Answer 29

• using finer particles means a larger surface area

- the extra surface area gives a faster reaction

Question 30

Describe the method used to show how temperature effects rate of reaction?

Answer 30

• sodium thiosulfate and hydrochloric acid are both clear solutions but react together to form a yellow precipitate of sulfur
• rate is measured by watching a black cross on paper underneath the conical flaks of solution disappear through the cloudy sulfur

Question 31

Describe the method used to show how a catalyst effects rate of reaction?

Answer 31

• set apparatus up with rthe catalyst (manganese powder) and hydrogen peroxide in a conical flask with a bung. Have a tube coming out of the bung to a gas syringe
• measure vol of gas produced in gas syringe at regular intervals
• repeat experiment using the same vol and conc of hydrogen peroxide but use a diff catalyst